All you need to do is simply go onto your server browser in Arma and hit filter.... then where it says host type in roleplay.co.uk and wait for the search to load until you find one of the roleplay.co.uk servers and hit connect on it.
Once you're connected select a civilian slot (Purple slot) and click an open slot and press join in the bottom right corner.... I recommend you spawn Kavala for your first time.
You can find multiple basic guides
here that include how to sign up for the police force and vehicle prices....
I highly recommend Stoneman's guide as its an interesting watch with a lot of comedy, Stoneman's video can be found
here (I recommend watching this as this will help you learn a lot while still being interested.... I learnt a lot of my friends the basics using this video
Make sure you read the rules as a lot of things are not allowed on the server and if you break one it could lead to a punishment.
Rules are found
here
Best of luck buddy! and I hope to see you in game. I recommend you sign up for the police because that's where a lot of players first start off with their experience to learn the rules on the server. I highly recommend it as it is a fun experience too and in my opinion, the quickest way to receive knowledge on the server, plus you will meet a lot of new great friends.
There are no downloads needed for the server as this server is fully vanilla. The only download required will be the mission file that will be installed when you first load into the game. No external downloads are required.